Process for dehydrating trialkali orthophosphate



March 1, 1938. A. WELTER 2,109,811

PROCESS FOR DEHYDRATING TRIALKALI ORTHOPHOSPHATE Filed Dec. 23, 1935 armBR1711731111111! ,IIJA'AWIJIIMIIM w l Patented Mar. 1, 1938 PROCESS FORDERAG 11 QBTHOPHQSIPTE aeou Welter, meme-mares, as

dpcation Dec In Ge w v This invention relates to a process fordehydrating trialkali orthophosphate, more particularly trisodiumorthophosphate, N&3PQ4, with ten or twelve molecules, i. e. with 52 or56%, of

5 water. The need for such an anhydrous salt has greatly increased inrecent years for use as an addition agent for soap, which is to be usedalso in hard water, but the drawback was discovered that the trialkaliphosphate retained the said very high water content so tenaciously' thatit was quite impossible in practice to efiect a complete drying.Furthermore, even a dehydration carried out only up to '7 or 8%, or evenup to about water content made the product so much more expensive thatthere were distinct limits to the possibilities of using the same.

In practice only two drying processes came for the most part intoconsideration, viz. drying on wicker-work in which operations had to becarried out very cautiously and slowly until finally eaking of the saltput a check to further drying,

and a whipping of the salt fused in its water of crystallization.However, this also could not be carried out up to the point of completedry-- 3 ing since the mass caked together before this and could not thenbe further stirred.

'Attempts have also already been made to atomize the salt in a cold orhot air stream without, however, producing thereby any removal of thewater of crystallization at all. The applicant has now discovered thatthe best results are obtained with the atomization process hitherto heldto be unutilizable for the dehydration of trisodium phosphate, and infact the watercontent isdiminished to only 2 to 3% with veryconsiderably diminished costs, it on the one hand the air stream withinwhich atomization is effected is heated to at least 60 C., whilst on theother hand a temperature of at least 130 C. is imparted to the atomizingair. The temperatures of the air stream and atomizing air do not exceed200 C. Only the conjunction of these two expedients, which have neverhitherto been taken into consideration renders possible this new verysurprising action at temperatures lying substantially below thetemperature limits which were thought to have been necessary for a.complete dehydration of the salt (according to Gmelin- Kraut 200 C.) andwhich practically were unutilizable.

According to the new process operations may also more particularly becarried out so that the salt to be atomized is fused in its own water ofcrystallization and is atomized out of the pressure vessel. For thispurpose salt which has been (ct. es-ier dried by centrifuging is fusedin autoclaves at about 10 atm. pressure and is atomized under thisintrinsic pressure. The hot air stream into which the atomization iscarried out may be produced in any desired way.

An apparatus for carrying out the new process is shown diagrammaticallyin the drawing. l is a a vessel in which the salt containing water ofcrystallization and to be atomized is melted or fused. 2 is a steamjacket having a steam inlet 10 3 and condensate separator t. 5 is theinlet for the salt coming from the centrifuge and only externally dry. tis a supply pipe for compressed air. I is an outlet for melted salt. tis an ascending pipe and t a further pipe for laterally 15 removing thecontent of the vessel 11 under pressure. A pipe l0 branches from thispipe downwardly. All pipes t to it are provided in. their exposed partswith heat insulating means i l.

Compressed air is admitted at it which comes W from a compressor notshown. The air is heated to the necessary degree in the coil it by meansof a steam jacket it. it is the corresponding steam trap. The dischargedhot air passes through pipe ill to the pipe 9, it and downwardly 25 tothe lower part of the section it. Pipes ll and it in the exposed sectionare protected against cooling by insulating means it. There is pro-.vided at the lower end of the pipes l0 and it the nozzle 20 where themelted or fused salt is atom- 30 ized by the hot compressed air in thetower 20. The atomized salt is collected at the bottom it of the towerM. An opening 23 allows of the discharge of the dry product.

Air passing throughthe tower 25 at M enters 35 a coil 25 and is stillcool, the said coil being surrounded by a steam jacket 26. Steam isadmitted at 27!; 28 is a condensate separator. Pipe it leads the heatedair to the tower 2|, whence it is discharged above at 30 and is conveyedthrough 4a the pipe 3! by the blower 32 into the open air and .issupplied to a washer not shown.

Such an apparatus may be supplied in any shape and size. It is onlynecessary that the fused or melted hot salt is atomized by hot air 45130 0., neither of the gas temperatures exceeda gas pressure andcontacting a stream of the ing 200 C.

2. A process for dehydrating trialkali orthophosphate consisting inatomizing a concentrated solution of the salt below 200 0. into a hotair stream having a temperature 01' at least 60 0., by contacting astream of said solution with a, stream of atomized air having atemperature or at least 130 0., neither oi the air temperaturesexceeding 200 0.

3. A process for dehydrating trialkali orthophosphate, consisting infusing 'the salt in its water 01' crystallization below 200 0. andcontacting the resulting liquid with a stream of gas of at least 130 C.so as to atomize the liquid into a hot air stream having a temperatureof at least 60 0., neither of the gas temperatures exoeeding 200 0.

4. A process for dehydrating trialkali orthophosphate, consisting infusing the salt in its water of crystallization below 200 0. and underresulting liquid with a stream or gas of at least 130 0., so as toatomize the liquid into a gas stream having a temperature of at least 600., neither of the gas temperatures exceeding 200' 0.

5. A process for dehydrating trialkali orthophosphate consisting infusing the salt in its ization of the latter.

ADOLF WELTER. 20

